Every man in the world likes to see another man's erection and to see him reach his orgasmic climax and ejaculate, not just gay and bisexual men. Looking at dicks is a guy thing not a gay thing and all men do it. The popularity of this site proves that.

As for erections and ejaculations, I think it comes down to the fact that neither can be faked. When we see sperm shooting out of an erect cock we know that it's the real thing.